The present invention relates generally to a keyboard apparatus used for electronic equipment such as personal computers, typewriters, calculators, word processors and the like, and, more particularly, to a key unit in a keyboard apparatus, as well as the keyboard apparatus itself, wherein the key unit is adapted to reduce the noise which is typically generated when a key unit is pushed or returns from the depressed position and hits the top plate of a keyboard or other type of shell around the key unit.
Keyboards are known as signal input devices that allow transmission of a relevant signal to a host device in response to the mechanical pressure being applied to a certain key unit out of a plurality of key units disposed in a predetermined positional relationship on a board in an electronic device or equipment. While keyboards are used in a variety of different electronic devices, the keyboards utilized in these devices usually perform the same function. Namely, an individual key unit of a plurality of key units of a keyboard usually consists of a key button that can be depressed by application of the mechanical pressure to the top of the key button, urging the key unit into movable contact with a contact point on a conductive membrane formed on a circuit substrate of the keyboard, which produces an electrical connection and causes a signal to be sent to the host device. Examples of various keyboard devices and their operation are well known in the art and disclosed in U.S. Pat. Nos. 4,677,600, 5,516,996 and 5,565,865.
Generally, there are many types of different key units that can be utilized in a keyboard. For example, U.S. Pat. No. 5,456,541 describes resilient rubber, spring and mechanical types of key units. Similarly, a resilient rubber key unit is described in U.S. Pat. No. 5,565,865.
In a conventional key unit, the key unit has a resilient pad, usually made of a resilient rubber or silicon rubber material, and a plastic keycap that is mounted on top of the resilient pad. The plastic keycap extends in the axial direction through the pre-determined opening in the top plate of the keyboard to accommodate the axial movement of the pad and keycap in response to the mechanical pressure in the axial direction that is applied by the keyboard operator to the top surface of the plastic keycap. The resilient pad is mounted over a conductive membrane sheet structure.
Electrical conductivity is provided in a conventional conductive membrane sheet structure below the resilient pad which is formed by stacking a lower sheet and an upper sheet, on which conduction layers are formed respectively. The bottom surface of the resilient pad has a stem portion that moves in unison with the pad in the axial direction and affects the contact between the fixed contact on the lower sheet of the conductive membrane sheet structure formed on a circuit substrate and the movable contact of the upper sheet. The upper and lower sheets of the conductive membrane sheet structure are separated from each other by a predetermined gap or an air pocket formed by the spacer inserted therebetween. When the stem portion of the resilient pad urges the movable contact of the upper sheet into physical contact with the fixed contact of the lower sheet an electrical circuit is established. Alternatively, electric conductivity is provided by a semi membrane or a PCB type of conductive membrane, which comprise a single conductive layer formed on a membrane sheet or circuit substrate. When the stem portion of the resilient pad is urged in the axial direction a conductive portion of the stem portion completes an electric circuit between a fixed row contact point and a fixed column contact point.
In addition, a conventional key unit may have a xe2x80x9cpre-loadedxe2x80x9d feature which is accomplished by using a flange on the keycap to limit the axial movement of the key unit. The flange contacts a pair of plastic ribs which are fixedly suspended from the inner surface of a top plate of the keyboard apparatus. These plastic ribs act as a stop and limit the axial movement of the key unit when it returns from a depressed position to its normal position.
The pre-loading is typically used to add stability and insure a constant height of the keycap. However, because the keycap is pre-loaded, each time a user depresses and thereafter releases the key unit, the flange of the keycap, strikes against the plastic ribs creating an undesirable impact and noise, often referred to as xe2x80x9cfeedback noise.xe2x80x9d Therefore, there is a need for an improved keyboard apparatus, in which the key units of the keyboard apparatus have the xe2x80x9cpre-loadedxe2x80x9d feature and associated advantages, but do not produce the impact and noise associated with the operation of conventional key units. Reduction of the impact and noise associated with the operation of keyboards in personal computers is particularly desirable because these devices are often used in enclosed public places, such as schoolrooms, on airplanes, and in large open office spaces that are subdivided into individual work areas, where the noise can be distracting and degrade productivity.
It is an object of the current invention to provide a keyboard apparatus that either eliminates or reduces the xe2x80x9cfeedback noisexe2x80x9d during its operation.
Another object of the current invention is to provide an improved key unit which may be one of a variety of different types that has xe2x80x9cpre-loadedxe2x80x9d functionality and eliminates the above-mentioned feedback noise and impact, thereby providing a cost-effective solution to keyboard manufacturers, without limiting them to only one type of key unit.
A further object of the present invention is to provide an improved key unit for various types of electronic devices that utilize a keyboard with one or a plurality of key units, where the improved key unit contains means for cushioning the impact of a key unit against the top enclosure of a keyboard, thereby eliminating the feedback noise, and at the same time retaining the benefits of a xe2x80x9cpre-loadedxe2x80x9d feature for a key unit.
These and other objects of the invention are accomplished by providing a key unit having at least one resilient bumper positioned on or extending from the key unit which cushions the impact of the key unit against the top plate of the keyboard when the key unit returns from a depressed position to a normal pre-loaded position. The resilient bumper may be incorporated in a variety of different types of key units such as a resilient rubber type, spring type, mechanical type or any other type of key unit that may or may not contain a plastic keycap that covers the movable portions or key pad of the key unit.
These and other objects of the invention are accomplished by providing a key unit that is able to assume a depressed position comprising in one embodiment a member movable in a defined direction in response to pressure, the member having at least one resilient bumper. The key unit is a component of an apparatus that has a stop that restricts the movement of the key unit when the key unit is returned from the depressed position. In addition, the bumper of the key unit is movable into contact with the stop of the apparatus when the key unit is pushed or returned from the depressed position.
These and other objects of the invention are accomplished by providing an apparatus comprising at least one such key unit.